I feel your pain. I'm on day 12 of SB and since I've started, I've rarely been able to eat more than 900 calories on any given day. I know that there is a limit on the number of nut servings that you're suppose to have in Phase 1, but in order to increase my calorie counts, I've been eating at least 2-3 servings of almonds and/or peanut butter daily. On days I'm really struggling for calories, I'll even throw in some avocado/guacamole.
As for what to do today, 900 calories is low, but if you're not hungry, I would go to sleep and when you get up tomorrow, try to add a few more servings of higher fat snacks throughout the day: add nuts to your cottage cheese and/yogurt; nuts and avocado to your salad, etc.
I hope this helps.